<!DOCTYPE html>
<meta charset=UTF-8>
<title>CSS Filter: Establishing containing block for absolutely-positioned elements, on an inline element</title>
<link rel="author" title="L. David Baron" href="https://dbaron.org/">
<link rel="author" title="Mozilla Corporation" href="http://mozilla.com/">
<meta name="flags" content="">
<style>

#cb {
    position: relative;
    filter: brightness(100%);
}

#abspos {
    position: absolute;
    top: 0;
    left: 0;
    width: 10px;
    height: 10px;
    background: blue;
}

</style>

<p>Filler text.</p>

<div>
    <span id="cb">Blue box should cover top-left corner of this sentence.<span id="abspos"></span></span>
</div>
